Awww poor baby. No wonder he is scared. I would be too if I was attacked and did not have the proper social skills or love from another human.

Before you decide to take him, please consider what you are going through right now with the ringworm. Personally I feel you have enough on your plate to deal with right now. That is just MHO.
Is it possible to look into an American Bulldog rescue in or around your area?
Can your friend keep him just a little while longer until some other arrangements can be made for this puppy?

Also, do you have the financial needs to get him to a vet to have his legs checked out? Maybe he has some nerve damage from the attack.
Don't get me wrong Tracy, I am not trying to discourage you on taking on this puppy, I just want you to see the overall view of this situation.